Depending on the extensions’ functionality and your business model, Plesk extensions can be distributed under various types of licenses.

Licence type Details
Free The users are not charged for using the extension. After it has been installed, all of its functionality is immediately available.
Single Offer

The users paying for such a license gain access to full functionality of the extension. Such a license is usually issued on a per-server basis.

An example of an extension with a “single offer” license could be an application that scans the server for vulnerabilities and reports them to the administrator.
Multiple Offers

This licensing model facilitates scalable (multi-tier) offers. It should be implemented when a Plesk administrator has the option of choosing one of the predefined sets of functions or available resources that this extension provides, which best suit their needs.

A good example is the Plesk Premium Email extension by Kolab. There, the administrator can choose which license to buy based on the desired number of user accounts.
Freemium Users are free to download and install the extension, and use a certain part of its functions. Additionally, they are offered to pay for access to its premium features. “Freemium” can be viewed as a combination of two types of licensing described above: “free”, and “single offer” or “multiple offers”.

Note: All extension licenses are in fact lease licenses, which means, they can only be purchased for a specific period of time (1 month). They are not perpetual licenses.

Note: An extension that requires a license to work can be installed on a Plesk server even without a license. This means, such an extension must be able to interact correctly with and without a license.

Single Offer Extensions

Extensions with a single offer license can be installed on the server but will not work without a purchased license.

License status Extension behavior requirements
License installed All extension’s functions are available
License not installed
  • Extension’s functions are unavailable;
  • Controls and screens pertaining to extension’s functions are inaccessible;
  • Attempts to access extension’s controls and screens pertaining to its functions result in displaying a “License required” message.

“License required” message example:

"The %%extension_name%% extension requires a license to function. You can purchase the license <a href="%%buy_url%%">here</a>."

Here, %%buy_url%% is the URL of the corresponding online store that sells the said license. This URL must be obtained from the extension’s metadata. Refer to the section Obtaining the Online Store URL Correctly for instructions.

Best practice:

The best way to communicate to the user the fact that the installed extension requires a license to function is to create a separate page dedicated to informing the user of the fact and explaining to the user the benefits of the extension.

The resulting page may look like this:

image 78789

Multiple Offers Extensions

Extensions with a multiple offers license can be installed on the server, will not work without a purchased license, and will enable different sets of functions or amounts of available resources depending on the installed license.

License status Extension behavior requirements

License installed,

resource limits not exhausted

 All extension’s functions defined by the license are available

License installed,

resource limits exhausted
  • Extension’s functions defined by the license are available within the resource limits, but no more;
  • Controls and screens pertaining to additional use of resources are inaccessible;
  • Attempts to access extension’s controls and screens pertaining to additional use of resources result in displaying a “Resource limits exhausted” message.
License not installed
  • Extension’s functions are unavailable;
  • Controls and screens pertaining to extension’s functions are inaccessible;
  • Attempts to access extension’s controls and screens pertaining to its functions result in displaying a “License required” message.

“License required” message example:

"The %%extension_name%% extension requires a license to function.
You can purchase the license <a href="%%buy_url%%">here</a>."

“Resource limits exhausted” message example:

"The limit of %%resource%% has been reached for the current %%extension_name%% extension license. You can upgrade your %%extension_name%% extension license <a href="%%buy_url%%">here</a>."

Here, %%buy_url%% is the URL of the corresponding online store that sells the said license. This URL must be obtained from the extension’s metadata. Refer to the section Obtaining the Online Store URL Correctly for instructions.

Freemium Extensions

A freemium extension provides some of its functions free of charge, using these functions requires no installed license. Access to full functionality of such an extension, however, requires a license to be purchased and installed.

License status Extension behavior requirements
License installed All extension’s functions are available
License not installed
  • Extension’s “free” functions are available;
  • Controls and screens pertaining to extension’s “premium” functions are visible to users but are disabled;
  • Attempts to access extension’s controls and screens pertaining to its “premium” functions result in displaying a “License required” message.

“License required” message example:

"This functionality is available only in the paid version of the %%extension_name%% extension. You can purchase the license <a href="%%buy_url%%">here</a>."

Here, %%buy_url%% is the URL of the corresponding online store that sells the said license. This URL must be obtained from the extension’s metadata. Refer to the section Obtaining the Online Store URL Correctly for instructions.